Anadromous migration of lamprey eels

Lampreys are another example of anadromous fish that have unique spawning habits. Sexually mature lampreys begin their migration upstream in late spring and early summer. During their upstream migration, they often use their large sucker-shaped mouths to attach themselves to large fish traveling in the same direction as them, and suck the meat of the attached fish as they travel upstream. Lampreys, like salmon, also change body color during reproduction, and the appearance of males and females is obviously different. The spawning ground is chosen in a clear and shallow river, with a sandy bottom and small pebbles, and a river section with a high flow rate. In such river bottoms, they transport small stones downstream to form a hollow nest. The shape of this nest is often oval or slightly round, about 1 meter in diameter, with a slightly concave bottom, and a pile behind the nest. Small stone.

After the male fish arrives at the spawning ground first, he starts to build a nest. Soon a female fish comes to help build the nest. They use their sucker-like mouths to suck up small stones, use dragging and vibration methods to loosen the small stones, and finally drag them to the back of the nest to build a pile. Sometimes a second female fish comes to help with the work, but this phenomenon is rare after all. The lamprey mating method is very interesting. The female first uses her mouth to attach to the big stone above the nest, and the male uses the same method to attach to the female's head. After that, the male wraps part of his body around the female. As a result, the two fish form an oval shape. Then, the male and female fish each violently vibrate the rear part of their body to stir up the fine sand, and at the same time, each releases eggs and sperm.

The surface of the eggs is sticky and can stick to sand and sink to the bottom of the nest. After the male and female fish release eggs and sperm, they separate and immediately transport the small stones above the nest to the pile of stones below. Due to the relationship between the water flow, more sand particles can be surged onto the nest, and the fertilized eggs can be transferred to the nest. Cover it up. This reproductive method is repeated in a short period of time until all the eggs in the female fish are discharged. At this point, the two parent fish leave to lay their ovaries. At this time, they are very tired from reproduction, and no matter what kind of enemy they are, they can catch them. Because during mating, the body is often injured, tissue damage and bacterial infection often make the extremely tired brood fish unable to recover and eventually die.

A European scholar named Wu Bin wrote a recital poem about the reproductive method of lampreys:

The occurrence of the eel clan is incredible,

They don't recognize each other, but they like to hug each other.

They bend their bodies and entangle themselves,

Weaving a knot of love, overlapping the slimy bodies;

Intimate competition, until foamy juice is produced,

Such seeds can give birth to things that wriggle.

They leave their future descendants without taking care of them,

But the porous sand holds foam-like droplets,

This hotbed can fertilize all accumulations,

The tiny eel will soon begin to crawl.

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